1. Field of the Invention
This invention relates to blower systems and blower control systems and, more particularly, to such systems for use in a ventilating installation for preventing surging while maintaining maximum efficiency of operation.
2. State of the Prior Art
Central air conditioning or ventilating installations, i.e., for both cooling and heating of air, as utilized in large buldings such as schools, office buildings and factories, typically utilize a central supply blower which is required to operate at a relatively high discharge pressure. Three inches to 30 inches of water are required to maintain an adequate flow rate of the air through the ventilating, i.e., air conditioning or heating, apparatus and ultimately through an arrangement of headers and dampers for distribution to the various individual rooms of the building supplied by the installations. As is also typical, a return is provided for exhausting air from the rooms and returning the thus exhausted air, usually mixed with a percentage of fresh air, through the air conditioning system to be recirculated.
A problem frequently encountered in such installations is known as surging. Very briefly, surging occurs when the supply flow rate diminishes but the discharge pressure remains relatively high. When this situation obtains, the supply blower stalls, in an aerodynamic sense, until the discharge pressure is reduced, at which time the supply blower again begins to generate a supply flow. If the required supply flow rate remains low, however, the discharge pressure again increases causing stalling to occur again. Unless controls are provided, the stalling repeats in a periodic manner until the system flow rate requirements increase. Numerous deleterious effects obtain from this surging condition. The resulting overloads on the blower, both as to the fan unit and the driving motor therefor, can destroy it. In addition, the periodic surging in the supply ducts which receive the discharge of the blower causes an undesirable bulging of the ducts with resultant, objectionable popping sounds, and may in fact destroy the ducts or substantially reduce their useful life.